IDENTIFICATION AND STRUCTURE OF THE NASR GENE ENCODING A NITRATE-RESPONSIVE AND NITRITE-RESPONSIVE POSITIVE REGULATOR OF NASFEDCBA (NITRATEASSIMILATION) OPERON EXPRESSION IN KLEBSIELLA-PNEUMONIAE M5AL

Klebsiella pneumoniae can use nitrate and nitrite as sole nitrogen sou rces through the nitrate assimilatory pathway. The structural genes fo r assimilatory nitrate and nitrite reductases together with genes nece ssary for nitrate transport form an operon, nasFEDCBA. Expression of t he nasF operon is regulated both by general nitrogen control and also by nitrate or nitrite induction. We have identified a gene, nasR, that is necessary for nitrate and nitrite induction. The nasR gene, locate d immediately upstream of the nasFEDCBA operon, encodes a 44-kDa prote in. The NasR protein shares carboxyl-terminal sequence similarity with the AmiR protein of Pseudomonas aeruginosa, the positive regulator of amiE (aliphatic amidase) gene expression. In addition, we present evi dence that the nasF operon is not autogenously regulated.